Gunmen loyal to Moammar Gadhafi crossed the border from Algeria to attack revolutionary forces in a border city, killing six people, a military official said Sunday.
Col. Ahmed Bani, a military spokesman for Libya's revolutionary forces, said the attack on Ghadames was on Saturday, but the gunmen had been crossing in cars filled with arms for several days.
He told reporters Sunday that the attackers belonged to a unit that had been under the command of Gadhafi's son, Khamis.
"These militias have attacked our people in Ghadames ... All the information we have got is that these groups are related to the son of Gadhafi, Khamis," Bani told a news conference in Tripoli.
"We are expecting some militias in that area to use the geographical base to hide in. Our freedom fighters have taken control of that area. Our freedom fighters will not allow (another attack)," he added.
An official from Ghadames, Ali al-Mana, confirmed the attack and said six people were killed and 63 others wounded.
The attack came as Libya's revolutionary forces said they had stepped up a siege around Gadhafi's hometown of Sirte in an attempt to wear down his loyalist forces inside.
The fighters have set up new roadblocks and checkpoints and posted snipers at key spots on Sunday.
The move comes after a heavy push by the fighters into the edge of the downtown that failed to dislodge Gadhafi's men inside Sirte on Saturday.
Seven fighters were killed and 150 were wounded in fierce street battles with Gadhafi's men.
The revolutionaries took Tripoli last month, effectively ending Gadhafi's rule and sending him into hiding.
But his loyalists still hold Sirte, as well as Bani Walid and pockets in south Libya.
Officer Osama Nuttawa al-Swehli said NATO hit four targets in Sirte in pre-dawn airstrikes.